AALTO UNIVERSITY SCHOOL OF CHEMICAL TECHNOLOGY
Degree Programme in Chemical Technology
CHEM-E3140 - Bioprocess technology II
DOWNSTREAM PROCESS:
LIQUID-LIQUID EXTRACTION
Group work report
Roshi Dahal
Kaniz Moriam
Paula Seppälä
Report submitted: 5.12.16
Abstract
Liquid -liquid extraction (LLE) is the process of separation of a liquid mixture of components
where liquid solvents are used followed by dilution of one or more components of the initial
mixture. This downstream process is significantly useful in Bioprocess technology. This is a
unit process which requires the knowledge of phase behavior and physicochemical
characterization of different compounds. This review summarizes the theory of LLE,
advantages and shortcomings of the process and its applications in different fields of
Bioprocess Technology.
TABLE OF CONTENTS
ABSTRACT
2
1. INTRODUCTION
4
2. THEORY
5
3. APPLICATIONS
7
4. CONCLUSIONS
8
REFERENCES
10
1. INTRODUCTION
Downstream processing refers to recovery and purification of chemicals, biosynthetic
products, pharmaceuticals, food from natural sources as animal, plant tissue or
fermentation process. It is one of the ways used to recover products from unwanted
metabolites for example by using filtration, distillation and separations via extraction.
These processes have been in use over a long period of time in chemical
engineering and bioprocess technology. In bioprocess technology, complications can
arise with the use of proteins, enzymes or other bio-molecules. The stability of these
molecules is one of the important aspects during the downstream process. [1]
Liquid-liquid extraction (LLE) is an important method to separate constituents
(solutes) of homogeneous liquid solutions. In this separation process, second liquid
solvent is added which is immiscible or partially miscible with the feed and the
solutes of the mixture are distributed between the two phases. A quantitative
measure of the how a component will distribute between the two phases is called the
distribution or partition coefficient. Distribution coefficient is the ratio of the
concentrations of the solute in the two different solvents when the system reaches
equilibrium. LLE as a method of separation is used if the distillation process is not
feasible, requires more energy or is too complex. LLE is also used if the material is
heat sensitive and non-volatile. [7]
2. THEORY
In liquid-liquid extraction, components in the fed material, consisting of liquid phases
are separated when third liquid also known as solvent is added to the process. By
adding this new component which is insoluble in the feed, a new phase is formed.
The component which is more important during the extraction or which is the desired
component to be extracted during the process is transferred to extract. The
remaining liquid from the feed which is separable goes to raffinate (fig.1).
The selection of solvent is one of the important issues. During the process, two liquid
phases are formed and both the components are differently distributed in solvent and
extract phases. The difference in phase compositions makes the mass transfer easy.
This distribution of the components in aqueous and organic phase is governed by
the distribution coefficient denoted by K. The distribution coefficient gives a
quantitative measure of how an organic compound will distribute between aqueous
and organic phases. K is the ratio of the solubility of solute dissolved in the organic
phase to the solubility of solute dissolved in aqueous phase. This means higher the
value of K, higher the solute will reside in the organic phase. If the separable
components’ boiling points vary, it makes the extraction beneficial. The difference in
density can make extraction easier, meaning; higher the difference in density
between the phases the extraction process is quicker. [2]
Fig.1: Liquid-Liquid extraction unit (source: CEP magazine, AICHE publications)
The extraction is carried out in two ways of mixing; countercurrent and co-current
mixing. The co-current flow is limited to one stage per extraction, whereas, counter
current is controlled as multi stages per unit. Depending on the density of the solvent
to the carrier liquid the counter current extraction can be carried out on two ways
(fig.2). If the solvent is less dense than carrier liquid, solvent is fed from the bottom.
In the mass transfer section, the solute is carried up to the top of extraction unit and
the carrier liquid is removed from the bottom. The reverse phenomenon happens if
the solvent is denser than the carrier liquid. The solvent is fed from the top of the
column and solute is carried down and carrier liquid is extracted from the top of the
extraction unit. [3]
Fig 2: Countercurrent extraction unit set-up in two different ways (source: CEP
magazine)
3. APPLICATIONS IN BIOPROCESS TECHNOLOGY
LLE has several applications in bioprocess technology and few of them are
explained in more detail in this chapter.
Fermentation and algae broths
Biofuels and chemicals produced during fermentation and algae are recovered and
purified by LLE process. During the fermentation of hydrolyzed lignocellulosic
biomass, important inhibitor such as phenolic compounds as well as higher alcohols
are removed by this process [11]. LLE is effective process for fermentation
technology due to the ability to reduce energy equipment as well as cost
effectiveness [4].
Removal of high boiling organics from wastewater
New technologies are developing day by day to reuse the water efficiently. Presence
of micro pollutant such aniline, phenols, nitrate aromatics have adverse effect which
renders the reuse of water. Solvent extraction method was reported as most
effective method to remove and recover these chemicals from the wastewater.
Several extractants including octanol, amines, cyanex, diethyl carbonate, ionic liquid
etc. has been employed to remove high boiling organics especially phenol from
wastewater. [5].
Removal of carboxylic acid
Acetic acid is produced during fermentation of yeast which is an important inhibiting
agents [11]. This acetic acid as well as other carboxylic acids and dicarboxylic acids
such as formic acid, succinic acid, valeric acid etc. are removed from aqueous
stream using LLE process. LLE process is more economical and less energy
consuming process compared to the distillation process [6].
Protein separation and purifications
Liquid -liquid extraction process is useful to separate and purify the protein and
peptides due to their more labile nature in the organic solvents. Different factors
affect the separation of protein using solvent extraction method including contact or
mixing of the phase, chemical properties of solvents, partitioning coefficients as well
as time of the extraction [7].
Essential oil extraction
Bio-oil is produced from biomass pyrolysis. The end product is a complex mixture of
different organic compounds. Due to high water content and high viscous property of
bio-oil, LLE method is an efficient process to separate bio-oil according to their
polarity and different chemical groups compared to the solid-phase extraction. The
effect of extraction solvent and volume ratio is significant in case of LLE of bio-oil [8].
Agricultural chemical extraction
Agricultural chemicals such as herbicides and pesticides are extracted from the
water using LLE method. Metals and mixture of organic compounds remains in the
agricultural waste are separated through the solvent extraction process [9].
Food industry applications
LLE process is commonly used in food industries. As for example, separation and
purification of a particular flavor or fragrance as well as caffeine extraction are done
by this process [12].
4. CONCLUSIONS
Liquid-liquid extraction is an efficient way of removing pollutants or products from an
aqueous mixture. It can be applied widely in different fields, for example in the
separation of hydrocarbons in petroleum industry, aromatics removal from fuel oils to
improve their burning qualities or in the extraction of phenol from coal tar liquor. LLE
is also applicable to many separation processes in the bioprocess technology field.
These include for example high boiling organics from wastewater, essential oil
extractions and protein purifications. [10]
The advantages of this process include its effectiveness towards compounds with
high boiling points even in low concentrations, azeotropic mixtures (mixtures with
points that when boiled, have the same composition in vapor than initially, thus
cannot be altered by simple distillation) and with heat sensitive compounds like large
organic molecules. Disadvantages are the large consumption of possibly toxic
solvent, which also when recycled in the system requires costly equipment. Thus,
right selection of the solvent in achieving a sustainable process is required and
creates challenges to the large-scale industry implementation of the process. [2]
If the aim of the process is to achieve a pure extract, the LLE as a downstream
process is most often only the initial step. Further purification, such as distillation,
crystallization or second extraction might be needed. This can heavily influence the
cost and complicity of the process design and has to be taken into consideration
when planning an overall efficient process. [10]
REFERENCES
1. NPTEL, Biotechnology, Downstream processing, Online material. Available
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Available
from
http://www.aiche.org/resources/publications/cep/2015/november/designprinciples-liquid-liquid-extraction
4. Birajdhar, S. D., Rajagopalan, S., Sawant, J.S., Padmanabhan, S.,
Continuous countercurrent liquid-liquid extraction method for the separation of
2,3-butanediol from fermentation broth using n-butanol and phosphate salt,
Process Biochemistry 50 (2015) 1449-1458.
5. Liu, J., Xie, J., Ren, Z., Zhang, W., Solvent Extraction of phenol with cumene
from wastewater, Desalination and Water treatment 51 (2013) pp 19-21
6. Mizzi, B., Meyer, M., Prat, L., Augier, F., Leinenkugel-le-cocq, D., General
design
methodology for reactive liquid-liquid extraction:Application to
dicarboxylic acid recovery in fermentation broth, Chem.Eng.Process(2016).
Available in http://dx.doi.org.libproxy.aalto.fi/10.1016/j.cep.2016.10.003
7. Kubek, D. J., “Liquid-liquid extraction”, in Protein Purification Process
Engineering , Rogger Harrison (ed.) Marcel Dekker, Inc. New York (1994) pp 87-91.
8. Wei, Y., Lei, H., Wang, L., Zhu, L., Zhang, X., Liu, Y., Chen, S., Ahring, B., Liquid
Liquid extraction of Biomass Pyrolysis Bio-oil, Energy Fuels 28 (2) (2014) pp 12071212.
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M.G., Extraction and characterization of Biomolecules from Agricultural Wastes,
Chemical Engineering Transactions 27 (2012) pp 331-335.
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Chemical Engineering Volume 2 - Particle Technology and Separation Processes
2001. 5th Edition. Elsevier Ltd.
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Wielen, L.A.M., Bont, J.A.M.,
Liquid- liquid Extraction of Fermentation inhibiting
Compounds in Lignocellulose Hydrolysate, Biotechnology and Bioengineering 102
(2008) pp 1354-1360.
12. Koch Modular Process Systems, LLC (KMPS), Industrial applications of
liquid -liquid extraction, Available from https://modularprocess.com/liquid-liquidextraction/industrial-applications/